Engine torque-detecting method and an apparatus therefor

Abstract

 A method and apparatus for measuring the instantaneous torque of an engine by measuring the change in pressure in the combustion chamber at two crank angles. The crank angles are chosen to approximate the time when the change in pressure is the greatest and when the pressure is the greatest and the change in pressure is zero. These crank angles may be either determined by measuring the values or by approximately the crank angles at which the values will exist. In some instances, the torque is measured by summing the change in pressures during the time interval and in other methods the torque is measured by determining the pressure difference at the two crank angles.

Description

[0001] This invention relates to an engine torque-detecting method and apparatus therefor, and more particularly to an improved method and apparatus for measuring engine torque during running.

[0002] It is well known to attempt to improve the efficiency and exhaust emission control of an internal combustion engine to operate it in such a manner as to accurately control the amount of fuel supplied to the engine. Also, other engine parameters are controlled in order to maintain good combustion with the minimum amount of fuel for environmental and efficiency reasons. In order to ensure stable running, however, it is necessary to ensure that adequate amounts of fuel are provided to the engine and that other running conditions are accurately controlled. Therefore, there is a need to measure the actual engine output so as to ensure stability in its operation.

[0003] For example, it is known that fuel economy and exhaust emission control may be achieved by operating the engine on a so-called "lean burn" system at least at low and partial lows. With lean burn running the fuel-air mixture supplied to the combustion chamber is less than stoichiometric. However, it is also known that the limits of lean burn may be readily determined by measuring the output torque of the engine. When the output torque falls below a predetermined value it is known that the stability and engine running speed will deteriorate significantly. Therefore, it is desirable to be able to measure the output torque of the engine during its running so as to permit optimization of the lean burn running.

[0004] Obviously, it is not possible to measure the engine output in the form of torque through the use of normal measuring apparatus employed for engine testing. That is, the torque-measuring devices used to determine the performance of the engine cannot be incorporated feasibly in a motor vehicle.

[0005] There have, therefore, been proposed methods for attempting to measure the engine output torque during its running by measuring some other parameter of the engine. It has been found that pressure in the combustion chamber can be utilized to project engine output torque and ensure stability in running. One method for measuring the engine output torque has been to sample the pressure readings at a number of output shaft angles during a single cycle of operation beginning near the end of the compression stroke and ending during the power or expansion stroke and then predict the engine torque from these readings. However, the necessity of taking multiple readings at varying crank angles provides a very complicated system, and normal computers cannot make the necessary calculations in the time period to adjust the engine to maintain stability without time lags. These problems are particularly acute when the engine is running at a high speed.

[0006] It has also been proposed to measure or estimate the output torque of the engine by measuring the peak combustion chamber pressure. Such a system obviously only requires one pressure reading. However, it has been found that this value is not as closely related to engine output torque as was thought, particularly when cycle-to-cycle measurements are being made and compared with each other.

[0007] In conjunction with measuring the torque of the engine and other engine measurements, it is desirable to be able to determine accurately the engine speed. It is commonly the practice to employ with engines a crankshaft or other shaft position detector that outputs a pulse when the shaft rotates to a particular angle. These sensors normally employ a permanent magnet and a related coil, in which the pulse is generated as the magnet and coil are brought into registry with each other. These sensors are normally employed not only to determine a reference angle position for the shaft, such a top dead centre, but also to measure engine speed by counting the number of pulses generated in a time period. Although these devices are particularly useful, they provide indications of average engine speed, and not engine speed during a single revolution or a portion of a revolution. With some measurements, such as the measurement of engine torque, it is desirable to measure the instantaneous angular rotational speed of the engine shaft during a single cycle of engine operation.

[0008] As has been previously noted, methods for determining or predicting engine torque have employed sensors for sensing the pressure in the combustion chamber. Such pressure sensors are well known and normally employ piezoelectric devices, which are exposed to the combustion chamber pressure. These devices actually output a first signal that is indictive of the change in pressure exerted on the piezoelectric device. An amplifier circuit is incorporated in conjunction with the piezoelectric device to receive the first signal and convert it into a second signal that will provide an actual pressure reading.

[0009] In some instances it is desirable to measure engine torque by actually measuring absolute pressure at certain time intervals. On the other hand, some torque measuring methods may be utilized to measure the accumulated pressure over a time period by integrating a differential pressure signal.

[0010] It is, therefore, a principal object of this invention to provide an improved method and apparatus for measuring the torque output of an engine during its running and per cycle.

[0011] It is a further object of this invention to provide an improved method and apparatus for measuring engine torque per cycle that can be utilized with a minimum number of readings.

[0012] Preferrably, said method using a pressure sensor should allow to derive either instantaneous change in pressure signals or absolute pressure signals.

[0013] Finally, the measuring apparatus of the present invention should allow to provide not only a reference signal indicative of engine shaft position, but should also allow to determine the instantaneous angular velocity of the engine shaft, preferrably in less than a complete revolution.

[0014] In order to perform said objectives the method for measuring the output torque of an internal combustion engine during a cycle of operation, according to the present invention, is improved by the steps of measuring the pressure and the combustion chamber between two output shaft angles during a cycle of operation and computing the torque of the engine from such measurements.

[0015] Thus, said combustion chamber pressure is measured between no more than two different crank angles and the engine output torque is determined from these two measurements.

[0016] In order to perform the afore-indicated objectives in terms of the apparatus, said measuring apparatus, according to the present invention is improved in that means are provided for eeading the combustion chamber pressure at two distinct crank angles and calculating the engine torque from these two readings. Preferrably, said apparatus comprises means for measuring the pressure in the combustion chamber and also means for measuring the output shaft angle.

[0017] In accordance with a preferred method embodying another feature of the invention, instantaneous engine speed for a portion of the rotation of the output shaft of an engine is measured. The engine comprises a shaft driven by the engine speed for a portion of the rotation of the output shaft of an engine is measured. The engine comprises a shaft driven by th engine and an assoicated fixed component of th engine that is juxtaposed to a portion of the shaft. A permanent magnet is fixed to one of the shaft portion and the component and a coil is fixed to the other of the shaft portion and the component and is adapted to output a pulse upon the passage of the coil and the permanent magnet upon rotation of the shaft for indicating the angular position of the shaft. The method comprises the steps of determining the shaft angle when the maximum positive pulse is generated by the coil, determining the shaft angle when the maximum negative pulse is generated by the coil, and measuring the time interval between the maximum positive and negative pulses to determine instantaneous shaft rotational speed.

[0018] Another preferred feature of the invention is adapted to be embodied in a method of sensing both absolute pressure in an engine combustion chamber and the instantaneous change in pressure. This method comprises a piezoelectric device that is adapted to be exposed to combustion chamber pressure and output a first electrical signal indicative of the change in pressure in the combustion chamber. An amplifier circuit receives the first electrical signal and transforms the first electrical signal into a second electrical signal indicative of the pressure in the combustion chamber. The method comprises the selection of one of the first or second electrical signals to determine either the change in pressure in the combustion chamber or the absolute pressure in the combustion chamber.

[0019] In the following the present invention is explained in greater detail by means of preferred embodiments thereof in conjunctioon with the accompanying drawings, wherein:

[0020] Figure 1 is a block diagram and partial schematic of an embodiment of the invention.

[0021] Figure 2 shows the time histories demonstrating operation of the embodiment of Figure 1.

[0022] Figure 3 shows crank angle histories of the combustion pressure Pϑ and dP/dϑ and the two detecting crank angles ϑ1, ϑ2 for the output torque (T).

[0023] Figure 4 is a block diagram of a second embodiment of the invention, whereby pressure and rate of pressure signals are used to determine the output torque (T).

[0024] Figure 5 is a third embodiment of the invention where one sensor value of either pressure P or dP/dϑ is predetermined and corresponds to a function represented in either Table 1 or 3.

[0025] Figure 6 is a fourth embodiment of the invention corresponding to functions represented in Table 2 and Formula 1.

[0026] Figure 7 is a fifth embodiment of the invention incorporating the functions in Table 4.

[0027] Figure 8 shows an alternate time T' of positive-to-negative pulses instead of the time between positive top dead centre pulses T; this corresponence is represented in Table 4.

[0028] Figure 9 shows alternate crank angles ϑ_i wherein the second angle is biased and the first angle is compensated as shown in Table 5.

[0029] Figure 10 shows alternate times T_i wherein the second time may be predetermined as shown in Table 6.

[0030] Figure 11 shows a Table 1 comprising sample functions to calculate detecting crank angles ϑ_i based on the engine speed R.

[0031] Figure 12 shows a Table 2 comprising sample functions to calculate detecting times T_i based on Formula 1, also a function of engine speed R.

[0032] Figure 13 shows a Table 3 comprising alternate functions for crank angles ϑ_i without the engine speed R.

[0033] Figure 14 shows a Table 4 comprising the derivation of alternate interval T' for positive-to-negative pulses using a predetermined angle ϑ_T,.

[0034] Figure 15 shows a Table 5 comprising the derivation of the first angle if the second angle is biased and refers to the embodiment of Figure 9, and

[0035] Figure 16 shows a Table 6 comprising the derivation of the first time if the second time is predetermined, as shown in the embodiment of Figure 10.

Detailed Description of the Embodiments

[0036] The measurement of the torque of an internal combustion engine for a motor vehicle is desirable for control of the fuel injection and ignition timing, control of the EGR flow rate, control of the secondary airflow rate to add to the exhaust gas, and, for an engine with variable valve timing, control of the opening and closing times of the intake and exhaust valves. Referring now in detail to Figure 1, a four-cycle engine is indicated generally by reference numeral 11 and is shown as a cross-section through a single cylinder. Since the internal details of the engine 11 are not necessary to understand the construction and operation of the invention, they will be described only summarily and by reference to a schematic drawing. Where a detailed description is omitted, it may be considered to be conventional.

[0037] The engine 11 includes a cylinder block 12 having one or more cylinder bores in which pistons 14 are supported for reciprocation. The pistons 14 and cylinder bores, as well as an attached cylinder head, define a combustion chamber 16. The pistons 14 areconnected by means of connecting rods 18 to the throws of a crankshaft, indicated generally by the reference numeral 20, and supported within a crankcase in a known manner.

[0038] A fuel-air charge is delivered to the combustion chambers 16 through an induction system that includes an air cleaner (not shown), which draws atmospheric air and delivers it to an induction manifold 22. A flow-controlling throttle valve 24 is provided in the induction manifold 22. This charge-forming system thus supplies an air charge to the intake manifold 22 and includes an electronically-opeated fuel injector 26 having a discharge nozzle (not shown) that sprays fuel into the intake manifold 22 downstream of the throttle valves 24. Although manifold injection is disclosed, it is to be understood that the invention may also be employed in conjunction with direct cylinder injection or other types of charge forming systems, such as carburetors or the like.

[0039] The charge formed in the induction system is then delivered to the combustion chamber through the intake manifold 22 and past the intake valve 28 operated by an overhead mounted camshaft (not shown). The charge is compressed in the combustion chambers 16. This charge is then fired by a spark plug 30 mounted in the cylinder head of the engine and having its spark plug 30 for its firing, and the ignition coil is controlled by an ignition circuit 32. The burnt charge is discharged past exhaust valves 39 operated by an overhead exhaust camshaft 36 to an exhaust system (not shown). The fuel injector 26 and ignition system are controlled by an air fuel ratio control unit, the construction of which should be considered to be conventional, and therefore details of its construction will not be discussed further except insofar as how the invention can be practised with such conventional control systems.

[0040] The engine torque-detecting system employs a pair of sensors comprised of a combustion chamber pressure sensor 38 which may be of the piezeolectric type and which produces a first electrical signal indicative of change in pressure and which is normally interconnected with a charge amplifier so as to produce an output second electrical signal indiccative of pressure. This pressure signal may be employed for certain tapes of controls but in accordance with a feature of the invention, the direct output of the piezoelectric device of the sensor 38 is employed for measuring the torque of the engine. By using the direct output of piezoelectric device, the output signal is indicative of a change or differential in pressure rather than absolute pressure and this is important in being able to practise the invention and measure output torque, as will be described.

[0041] In addition, the engine is provided with a crank reference angle sensor which is employed to provide signals for other controls for the engine indicative of position of the shaft or by counting the pulses in a given time the average should be determined. In conjunction with the torque measuring aspect, theoutput of this position sensor is utilized so as to measure engine speed during single cylcle of opeation so as to permit the accurate determination of the engine output torque. Again, this will be described in more detail later but in accordance with a feature of the invention the reference angle signal is associated with one of the camshafts, in this case the exhaust camshaft 36 which like the intake camshaft (not shown) is driven in a suitable manner from the crankshaft 20 at one-half crankshaft speed. By operating this sensor from the camshaft rather than the crankshaft it is possible to measure the speed at top dead centre at the time when combustion is occuring without having to discrimate between the cycle when the engine fires and the portion of the cycle when the engine does not fire.

[0042] It has been determined that the engine output torque may be accurately determined during each cycle of operation of the engien by taking measurements at 2 finite crank angle or time positions and either integrating the output of the piezoelectric sensor 38 during this time period or actually comparign actual pressure measurements at the two time periods when the change in combustion chamber pressure in relation to time (dP/dt) is at its maximum (pressure increase rate is the greatest) and at another time when the change in pressure in relation to time (dP/dt) is zero (this being the point of maximum pressure, as will be seen hereinafter). Also, rather than measuring the initial time t₁ when the change in pressure is th greatest, it is possible to make a calcculation indicative of the crank angle position when this condition will occur, as will become apparent by the following description.

[0043] Referring now again to Figure 1, the engine control unit 42, or CPU, may be of the preferred construction as shown. Other engine control or protection systems may be incorporated in the CPU 42, but these embodiments will not be detailed in the discussion of the present invention which deals only with the way engine torque is measured to permit lean burn operation with maximum stability. Of course other applications for this principle will present themselves to those skilled in the art.

[0044] As shown in Figure 1, the CPU 42 may first include a means 44 to determine the reference crank angle ϑ₀ occuring at the time t₀. Second, a means 46 to calculate the reference time L for the engine to rotate through a known angle and hence instantaneous speed N_s. Third, a means 48 to calculate the time D from the reference crank angle position t₀ to the time t₁ where it will be known that dP/dt is maximum. From the calculation of the time D it is possible to determine at the stage 50 of the CPU 42 the time t₁ when the change in pressure is maximum.

[0045] These relationships can be best understood by reference to Figure 2 which shows, among other things, the output signal from the crank or camshaft angle sensor 40 (curve A). The camshaft angle sensor 40 is comprised of a permanent magnet that is affixed at a point on the camshaft 36 which is indicative of top dead centre position after the intake valve has closed and when combustion either has been initiated. This magnet cooperates with a winding that is fixed relative to the engine in proximity to the camshaft 36 and which will out put first a positive output signal when the magnet passes it and then a signal whcih dimishes to a maximum negative value when the camshaft 36 has rotated through a predetermined crank angle ϑ from the initial crank angle ϑ₀ at the time T₀. This rotational angle ϑ_N is then used at the stage 46 so as to determine the time duration L that it takes the engine shaft (camshaft 36 in this embodiment) to rotate through this angle and this speed N_s. This time is calculated by using a timer that outputs a number of equal time pulses and the number of pulses for the camshaft to rotate through the angle ϑ_N is determined by the output of the counter. This in essence gives an instantaneous crankshaft speed and the time period L can be employed to determine from known parameters the time delay D after T₀ when the maximum change in pressure in relation will occur from the equation:

[0046] In the foregoing equation, the factors f, r, and c are all constants which can be determined experimentally.

[0047] As has been previously noted, it would be possible to measure the point t₁ by checking the output of the piezoelectric part of the pressure sensor 38, but it is equally as acceptable to calculate this time from the aforenoted equation and thus simplify the overall control circuitry.

[0048] Thus, at the stage 50 of the CPU 42 the time t₁ is calculated as being equal to the following equation:

[0049] This time signal t₁ is outputted to an integrating circuit 54 so as to open a gate and permit this integrating circuit 54 to receive the output signal from the piezoelectric device of the pressure sensor 38 so as to perform an integrating function as follows:

[0050] This integrating circuit 54 is shut off by a shut-off device 52 which shuts off the gate when the output from the piezoelectric device of the pressure sensor 38 indicates that dP/dt = 0, this being the time t₂ on the pressure curve shown in the Figure 2C and also the time when the change in pressure from the combustion chamber pressure sensor 38 in relation to time reaches 0. This time. interval G is also equal to L·w where w is a constant and L is the value previously calculated by determining the speed of rotation of the camshaft.

[0051] The integrating function occurring at the stage 54 thus calculates output torque from an equation that can be determined experimentally and then output signals are outputted to a fuel control circuit, indicated at 56 and an ignition timing control circuit 58 which controls the firing of the spark plug 30 through the ignition circuit 32. This can be done in accordance with any desired control strategy.

[0052] In the previously described embodiment, two specific time intervals were chosen depending upon the rate of change of pressure in the combustion chamber and the pressure variations during this time pcriod were integrated to determine torque. It has also been determined that torque can be accurately determined by measuring the actual difference in pressure signals from the pressure sensor 38 at two different time intervals or degrees of crankshaft rotation during each cycle of engine operation so long as the angular positions are accurately chosen. These two crankshaft measurement angles ϑ₁ and ϑ₂ may be determined to be the points in time when the change in pressure in relation to time or crank angle is at a maximum and 0, respectively as with the previously described embodiments. These points are not determined by actual pressure measurements but merely by crank angles. This may be seen by reference to Figure 3 which shows the combustion pressures as functions of the crank angles ϑ_i. The first angle ϑ₁ may be chosen as the position near to the top dead center (TDC) of the piston stroke; the other angle ϑ₂ may be 10 to 20 degrees after the TDC. Here, ϑ₁ is the crank angle corresponding to time t₁ and crank angle ϑ₂ corresponds to time t₂. The pressure differential dP/dϑ may then be derived from the aforementioned angle-time relationships and shown as in the lower curve of Figure 3, as a function of crank angle ϑ.

[0053] In determining the time or crank angles ϑ₁ and ϑ₂ when the pressure measurements are made it has to be borne in mind that the change in pressure in the combustion chamber is a function of when spark timing occurs. That is, the pressure begins to rise rapidly whence the spark plug is fired after the intake valve has been closed. Thus, in order to practice this embodiment of the invention it is desirable to vary the angles ϑ₁ and ϑ₂ in response to the change in spark timing. Most engines operate with timing curves that vary in relation to engine speed R and hence the shift in the measurement angles ϑ₁ and ϑ₂ can be varied in response to engine speed. Table 1 shows a number of variations in which this may be done in relation to engine speed R. In this table the values of ϑ_x, α, β and φ are constant and ϑ₀ is the reference angle position when the camshaft position sensor 40 outputs its maximum plus signal as seen in Figure 2A.

[0054] It is also possible to practice the invention by actually measuring the points when the change in pressure in relation to time or crank angle is the maximum and when it is 0 by actually measuring these conditions. As has been noted, the output of the piezoelectric sensor portion of the pressure sensor 38, shown schematically at 139 in Figure 4 is indicative of dP/dt while the actual output of the sensor and its amplifier, indicatcd schematically at 138 in Figure 4 is indicative of the actual combustion chamber pressure P. The system shown in Figure 4 can be employed to measure the pressure at the maximum pressure change condition and the second maximum pressure by actually determining when these pressure conditions occur. This is done by using the pressure value detected by the pressure sensor 138, when the value dP/dt detected by the dP/dt sensor 139 is maximum and a maximum pressure when the value of the dP/dt sensor 139 is zero. The estimated output torque [T] is then calculated by the difference between the higher pressure and the lower pressure.

[0055] The structure for doing this is as shown in Figure 4. An analog-to-digital converter (A/D) 142, is used to provide digitized input to a data converter 144, which generates the parameters as a function of the crank angle ϑ. These parameters, P(ϑ) and dP/dϑ(ϑ), are used by a data selector means 146 to determine the values P(ϑ₁) and P(ϑ₂). These values at the appropriate angle times may then be incorporated in the calculating elements 148, 150 to generate the difference between these pressures, which is used to calculate engine torque [T].

[0056] Of course, in the system shown in Figure 4, the computer must have a program and memories to determine when the value dP/dt is maximum and also if it is 0 so as to select the two measurements at the points ϑ₁ and ϑ₂ as shown in Figure 4. Of course, this is well within the scope of those skilled in the computer art.

[0057] As has been noted in conjunction with the description of the embodiment involving the use of Table 1, it is possible to have the system merely preprogrammed for the angles ϑ₁ and ϑ₂ when the pressure or change in pressure measurements are made. These points in time can be determined experimentally by actual engine testing and then programmed into the computer. Such another embodiment of the invention is depicted in Figure 5, whereby the crank angles ϑ_i for the detecting pressures, or the detecting times, are based on the engine speed R. A TDC angle sensor 240 is utilized in conjunction with a chamber pressure sensor 238 and a A/D element 242 to generate the digital signals. A data converter 244 next generates the pressure as a function of crank angle ϑ, while a calculating means 243 generates the engine speed R, which may be determined as a function of the interval of the dead center pulses. Sample values of the functions for the crank angles ϑ₁ and ϑ₂ may be as shown in Table 1, and the values for constants α, β and γ are kept in a memory element 245. The functions shown in Table 1 may then be combined with the engine speed information in a calculating element 247; the resultant angles ϑ₁ and ϑ₂ are then utilized in a data selector unit 246, which determines the corresponding pressures at those angles. Calculating means 248, 250 then generate the difference between the pressures to output the estimated engine torque [T].

[0058] In the embodiment shown in Figure 5, the system operates by having a series of measured crank angles at which point the pressure or change in pressure must be measured in order to obtain the torque reading.

[0059] The embodiment of Figure 6 does not utilize engine speed information. A TDC angle sensor 340 and a chamber pressure sensor 338 are processed by an A/D unit 342 to generate digitized values; the discrete anglc sensor value is then used to generate a reference time T in a calculating element 343 based on Formula 1, wherein µ and ν are constants. As shown in Table 2, sample functions are used to determine the times for the detecting crank angles ϑ₁ and ϑ₂, which are based on predetermined constants µ, ν, γ and κ. These values are stored in a memory 345 and used in a calculating means 347 to determine times T_ϑ1 and T_ϑ2 for the corresponding angles ϑ₁ and ϑ₂. A data selector unit 346 next determines the pressures at the selected times of the selected crank angles, which pressures then go into calculating means 348,350 to determine the difference in the pressures and the estimated engine torque [T].

[0060] In the discussion previously when reference has been made to engine speed R, the engine speed R has been generally considered the speed that requires the engine to rotate through a complete or series of revolutions. The normal output pulses from a crankshaft rotational speed sensor are measured and summed in a time period to dctcrmine engine speed as shown by the distance T in Figure 8 which shows successive pulses during a complete revolution either of the crankshaft or, in the embodiments as described, of the camshaft. However, as was noted in the earlier discussion, it is possible to make an instantaneous time determination T' of a shorter time interval between when the output pulse is at a maximum and minimum. This may be utilized to shorten the sample time interval required for the aforementioned calculations and if this data is used, then some of the tables must be modified for this measure of calculation. See for example Table 3 that could be utilized with the embodiment of Figure 5 wherein different values are given for the variable constants dependent upon this information. By the way, such a system can also be used for detecting engine speed outside the area of detecting the engine torque.

[0061] An embodiment using this time T' is shown in Figure 7, whereby a crank angle sensor 440 is utilized along with a pressure rate sensor 439. The values are processed through an A/D unit 442, and the resulting digitized angle is processed in a detector element for T' 443.

[0062] Referring to Table 4, a value for T is determined in a calculating means 444. Referring again to Table 2, the constants µ, ν, γ and κ, in a memory 445, are utilized with time T in a calculating element 447 to generate the times T_ϑi for angles ϑ₁ and ϑ₂. An integrating element 449 is utilized to determine the pressures at the crank angle times by integrating the rate values from the time T_{ϑ2 to the} T_ϑ2 directly to output the signal P_(TO1) - P_(TO2) to the calculating means 450. Calculating means 450 determines the estimated engine torque value [T] from this data.

[0063] As previously noted, because the ignition timing is controlled relative to the engine speed R, it is shown in Table 1 that the crank angles for the detecting pressures, or the detecting times, may be chosen by the CPU 42 based upon the engine speed R, and at a low engine speed both of the times or angles may be delayed, while at a high engine speed they may be advanced. As shown in Table 1, ϑ_x, α, β, and γ are all constant values. The detecting crank angles may be changed as shown in Figure 9 and Table 5. If a second detecting crank angle ϑ₂ is biased by a delta value (Δϑ), the first detecting crank angle would then be advanced by a value equal to a constant C multiplied by this delta value, where C is a value less than one.

[0064] Similarly, as shown in Figure 10 and Table 6, the detecting times may be changed. A calculating program may choose T_ϑ'2 or T_ϑ''2 (which is predetermined) instead of T_ϑ2 as a second detecting time. In this case, T_ϑ'1 must be used as the first detecting time.

[0065] The preferred and alternate embodiments previously described demonstrate that the use of one or two crank angle sensors yields several possibilities for the generation of an engine torque value. It has also been indicated that the crank angle sensor, in addition to providing a signal indicative of crank angle, can be utilized to provide an indication of accurate instantaneous engine shaft speed. Although in the illustrated embodiments this has been done with one sensor, it is to be understood that a number of such sensors may be positioned at spaced intervals around the shaft so as to measure instantaneous shaft speeds at desired shaft angles.

[0066] Various other changes and modifications may be made from the embodiments presented herein without departure from the spirit and scope of the invention, as defined by the appended claims.

[0067] Moreover, both the absolute pressure in the combustion chamber and its instantaneous change can be sensed by means of a piezoelectric device adopted to be exposed to combustion chamber pressure and outputting a first electrical signal indicative of the change in pressure in the combustion chamber. An amplifier circuit receives the first electrical signal and transformes same into a second electrical signal indicative of the pressure in the combustion chamber, while one of said first and second electrical signals is read for either representing a change in combustion chamber pressure or an absolute pressure signal.

[0068] In the aforegoing description reference is made to the following Tables:

[0069] The system has two functions to calculate ϑ₁ and ϑ₂. Within the above sample functions two functions can be choosen.

[0070] ϑ_x, α, β, γ are constants.
R is engine speed (RPM).

Formula 1:

[0071] 

Claims

1. A method for measuring the output torque of an internal combustion engine during a cycle of operation wherein the engine comprises a combustion chamber and an output shaft driven by combustion ocurring in the combustion chamber said method comprising the steps of measuring the pressure in the combustion chamber between two output-shaft angles during a cycle of operation and computing the torque of the engine from such measurements.

2. A method as claimed in claim 1, wherein the change in pressure in the combustion chamber is measured.

3. A method as claimed in claims 1 or 2, wherein the torque is computed by summing the changes in pressure during the time period between the two output shaft angles.

4. A method as claimed in at least one of the preceding claims 1 to 3, wherein one of the output shaft angles is the angle when the change in pressure is the greatest.

5. A method as claimed in at least one of the preceding claims 1 to 4, wherein the other output shaft angle is the output shaft angle where the maximum pressure exists and the rate of change of pressure is zero.

6. A method as set forth in at least one of the preceding claims 1 to 5, wherein one of the output shaft angles, preferrably the first output shaft angle is computed from known data.

7. A method as claimed in claim 6, wherein the computed angle is computed by determining the speed of rotation of the output shaft.

8. A method as set forth in claim 7, wherein the speed of rotation of the output shaft is measured from a sensor that provides a single pulse during one rotation of the shaft.

9. A method as claimed in claim 8, wherein the speed is calculated by measuring the angular rotational speed of the output shaft for less than one complete revolution by sensing the change of the pulse and determining the angle which the shaft rotates for the pulse to change.

10. A method as claimed in claim 1, wherein the actual pressure in the combustion chamber is measured.

11. The method as set forth in claim 10, wherein the torque is determined by measuring the differences in pressure in the combustion chamber at the two output shaft angles.

12. A method as claimed in at least one of the preceding claims 1, 10 or 11, wherein the two output shaft angles are selected as an angle immediately before top dead centre and another angle in the range of 10° to 20° after top dead centre.

13. A method as claimed in at least one of the preceding claims 1 to 12, wherein the selected output shaft angles are varied depending upon the speed of the engine.

14. A method as set forth in claim 13, wherein the engine is a spark ignited engine and the spark timing is also varied with engine speed.

15. A method as claimed in at least one of the preceding claims 9 to 14 measuring instantaneous engine speed for a portion of rotation of an output shaft of an engine comprising a shaft driven by the engine and an associated fixed component of the engine juxtaposed to a portion of the shaft, a permanent magnet fixed to one of the shaft and the component and an electrical coil fixed to the other of the shaft and the component and adapted to output a pulse upon passage of the coil and the permanent magnet upon rotation of the shaft for indicating the angular position of the shaft, said method comprising the further steps of determining the shaft angle when the maximum positive pulse is generated by the coil, determining the shaft angle when the maximum negative pulse is generated by the coil, and measuring the time interval between the maximum positive and negative pulses to determine instantaneous shaft rotational speed.

16. A method as claimed in claim 15, wherein the engine is a four-cycle engine.

17. A method as claimed in claims 15 or 16, wherein the shaft comprises a cam shaft driven by the engine crankshaft and rotating at one-half crankshaft speed.

18. A method as claimed in at least one of the preceding claims 15 to 17, wherein the coil and permanent magnet are disposed to provide an indication of top dead centre.

19. A method as claimed in at least one of the preceding claims 15 to 18, further comprising determining the actual shaft angle from the output pulse and summing the output pulses for a given time period to determine average shaft rotational speed.

20. A method as claimed in at least one of the preceding claims 1 to 19, characterised by sensing both absolute pressure in an engine combustion chamber and its instantaneous change of pressure comprising a piezoelectric device adapted to be exposed to combustion chamber pressure and outputting a first electrical signal indicative of the change in pressure in the combustion chamber, and an amplifier circuit receiving the first electrical signal and transforming the first electrical signal into a second electrical signal indicative of the pressure in the combustion chamber, said method comprising the further step of selecting which of said electrical signals is read to provide either a change in pressure signal or an absolute pressure signal.

21. A method as claimed in claim 20, wherein the method further comprises summing the first electrical signals for a given time period to determine engine torque.

22. A method as claimed in claims 20 or 21, wherein the time period is selected to begin at the time when the change in pressure is at a maximum and end the summing when the change in pressure is zero.

23. An apparatus for measuring the torque of an internal combustion engine specifically for performing the method according to claim 1, comprising a combustion chamber, an output shaft driven by combustion in the combustion chamber, means for measuring pressure in said combustion chamber from said pressure sensor between two distinct output shaft angles during a cycle of operation and computing the engine output torque from said pressure measurements.

24. An apparatus as claimed in claim 23, wherein the change in pressure in the combustion chamber is measured.

25. An apparatus as claimed in claims 23 and 24, wherein the torque is computed by an integrator that integrates the changes in pressure during the time period between the two output shaft angles.

26. An apparatus as claimed in at least one of the preceding claims 23 to 25, wherein one of the output shaft angles is the angle when the change in pressure is the greatest.

27. The apparatus as claimed in claim 26, wherein the other output shaft angle is the output shaft angle where the maximum pressure exists and the rate of change of pressure is zero.

28. The apparatus as set forth in claim 27, wherein the speed sensor provides a single pulse during one rotation of the shaft.

29. The apparatus as claimed in claim 27, wherein the speed is calculated by measuring the angular rotational speed of the shaft for less than one complete revolution by sensing the change of the pulse and determing the angle which the shaft rotates for the pulse to change.

30. The apparatus as claimed in claim 23, wherein the actual pressure in the combustion chamber at the two output shaft angles.

31. The apparatus as claimed in claim 30, wherein the torque is determined by measuring the differences in pressure in the combustion chamber at the two output shaft angles.

32. The apparatus as claimed in at least one of the preceding claims 23 to 31, wherein the two output shaft angles are selected as an angle immediately before top dead centre and another angle in the range of 10° to 20° after top dead centre.

33. The apparatus as set forth in at least one of the preceding claims 27 to 32, wherein the selected output shaft angles are varied depending upon the speed of the engine.

Drawing